In web conveyor devices wherein a roll-shaped physical object such as paper, film, cellophane, metal foil, rubber, or the like (hereinafter termed a “web”) is fed out from a feeding portion, specific processes are performed on the web, and the web is then taken up, in a receiving portion, after processing, there have been proposals for the velocity measuring devices for measuring the surface velocity of the web. See, for example, Japanese Unexamined Patent Application Publication No. 2011-141128 (the “JP '128”).
When measuring deviations in surface velocity using the technology disclosed in the JP '128, the deviation is calculated from differences in the surface velocity. However, when the difference for which the measurement is attempted is small when compared to the absolute value of the surface velocity, the errors included in the measured values for the surface velocities will be large relative to the difference between the surface velocities, and thus there is a problem in that this reduces the accuracy of the measurement of the deviation.
The JP '128 is a Doppler velocity meter as another velocity measuring device. The Doppler velocity meter is essentially identical to the self-coupling laser sensor disclosed in the JP '128 in the point that a frequency deviation, known as a Doppler shift, that is proportional to the velocity is produced, and thus when the deviation is calculated from the difference between the velocities the same problem as described above will occur.
In addition, Doppler velocity meters, which generally use frequency analysis, such as FFT (Fast Fourier Transforms) have issues such as the following in signal processing. The frequency resolution (velocity resolution) in FFT is determined by the length of the sampling interval, so a long sampling interval is required for high resolution, and, at the same time, it is necessary for the signal frequency to be constant during the sampling interval. The velocity deviation during the sample interval appears as a spreading of the frequency strength peak, and an error results when the power spectrum average does not match the average frequency (velocity) during the sampling interval. The reason for this is that the FFT expresses the average signal strength, rather than expressing the temporal distribution of the primary signal frequency, on the time axis, so that it will be pulled to frequencies wherein the signal strength is strong after application of the window function. Consequently, velocity deviation measurements using FFT have major problems.
Furthermore, because in FFT the number of samples required is determined by the maximum frequency that is subject to analysis and the resolution, the same sampling data are required whether the physical quantity being calculated is the absolute velocity or the velocity deviation. That is, in order to calculate fine deviations in velocity data with a high sampling frequency over a long time window length are required commensurate with the velocity resolution. The calculation overhead required by FFT becomes massive, making it impractical.
Moreover, as a technology related to the JP '128, there is the signal count correcting technology that uses a binary signal for a periodic signal. See, for example, Japanese Unexamined Patent Application Publication No. 2011-033525 (the “JP '525”). This technology disclosed in the JP '525 is a technology that both has an excellent capability for separating signal from noise, and performs signal processing quickly with high accuracy; however, when the signal quality is remarkably poor, so that the signal and noise cannot be separated completely so that the accuracy of the measured value for the velocity is reduced, the error included in the result of the measurement of deviation calculated from the difference between the velocities that include measurement error will be relatively large when compared to the magnitude of deviation, producing a remarkable reduction in the accuracy of measurement of the deviation.
As described above, in the conventional technologies there are problems in that it is difficult to improve the accuracy of measurement of deviation when attempts are made to calculate the deviation in surface velocity from differences in surface velocities of the object.
The present invention was created in order to solve the problems set forth above, and an aspect is to provide a velocity deviation measuring device and method that enables an improvement in the accuracy of measurement of deviation of surface velocities.